Approaching antioxidants
research has failed to find consistent effect on disease prevention
in man. A European study reveals some factors which could be
hampering successful trials.
Dietary antioxidants may be able to regulate multiple key cellular processes, including cell proliferation and apoptosis, according to scientists taking part in a recently completed EU-funded project. This has important implications for understanding the development and prevention of major diseases.
Epidemiological studies show that populations consuming diets rich in plant foods have a reduced risk of degenerative diseases. The attention of many researchers has therefore focused on components of foods that have antioxidant properties, for instance vitamins E and C, beta-carotene, and many phytochemicals such as flavonoids. However, intervention studies have not shown a consistent benefit of increased intake of dietary antioxidants.
There has been much debate about antioxidants in recent months, with a recent study appearing to confirm the lack of action antioxidants have on heart disease outcome. The 'Eurofeda' review highlights key areas warranting further research which could help inform future trials on the benefits of antioxidants.
Eurofeda participants worked in three task groups, aiming to identify the most reliable biomarkers of oxidative damage, assess what is known about the bioavailability of dietary antioxidants, and determine the role of dietary antioxidants in minimising oxidative damage and in gene expression.
The groups reviewed evidence based on recent research linking functional effects of dietary antioxidants at the molecular, cellular, tissue and whole body level with human health and disease.
They found that many of the biomarker studies examined had used invalid assays and/or unstable, non-specific biomarkers (a change in a biological molecule or metabolic process) that had little, if any, relevance to human disease.
Studies provided evidence that many dietary antioxidants can pass from the gut into the bloodstream and that the antioxidant capacity of the blood is increased as a result, but the biological implications of this are unclear, said the researchers. With few exceptions, little is known about the extent to which they are then subsequently transported to body tissues and metabolised.
They also reported that the majority of data demonstrating that changes in gene expression can be modified by antioxidants was obtained from animal and cell models, using nutritionally irrelevant doses. This means that the relevance of such data in man is unknown.
The Eurofeda review is published in Molecular Aspects of Medicine, vol 23, numbers 1/3.
